Evaporative Emission (EVAP) Leak Check Monitor

Some vehicle applications with the EONV EVAP leak check monitor use a remote in-line FTP sensor.
If the target pressure or vacuum on the fuel tank is achieved within the calibrated amount of time, the
test is complete.
4. The EONV EVAP leak check monitor uses the naturally occurring change in fuel tank pressure as a
means to detect a leak in the EVAP system. At key off, a target pressure and vacuum is determined
by the PCM. These target values are based on the fuel level and the ambient temperature at key off.
As the fuel tank temperature increases, the pressure in the tank increases and as the temperature
decreases a vacuum develops. If a leak is present in the EVAP system the fuel tank pressure or
vacuum does not exceed the target value during the testing time period. The EONV EVAP leak check
monitor begins at key off.
After key off the normally open canister vent (CV) remains open for a calibrated amount of time to
allow the fuel tank pressure to stabilize with the atmosphere. During this time period the FTP sensor
is monitored for an increase in pressure. If pressure remains below a calibrated limit the CV is closed
by the PCM (100% duty cycle) and seals the EVAP system from the atmosphere.
If the pressure on the fuel tank decreases after the EVAP system is sealed, the EONV EVAP leak
check monitor begins to monitor the fuel tank pressure. When the target vacuum is exceeded within
the calibrated amount of time the test completes and the fuel tank pressure and time since key off
information is stored. If the target vacuum is not reached in the calibrated amount of time, a leak is
suspected and the fuel tank pressure and time since key off information is stored.
If the pressure on the fuel tank increases after the EVAP system is sealed, but does not exceed the
target pressure within a calibrated amount of time the CV is opened to allow the fuel tank pressure to
again stabilize with the atmosphere. After a calibrated amount of time the CV is closed by the PCM
and seals the EVAP system. When the fuel tank pressure exceeds either the target pressure or
vacuum within the calibrated amount of time the test completes and the fuel tank pressure and time
since key off information is stored. If the target pressure or vacuum is not reached in the calibrated
amount of time, a leak is suspected and the fuel tank pressure and time since key off information is
stored.
When a leak is suspected, the PCM uses the stored fuel tank pressure and time since key off
information from an average run of 4 tests to suspect a leak. Some vehicles use an alternative
method of a single run of 5 tests to determine the presence of a leak. If a leak is still suspected after 2
consecutive runs of 4 tests, (8 total tests) or 1 run of 5 tests, DTC P0456 is set and the MIL is
illuminated.
5. The EONV EVAP leak check monitor is controlled by a separate low power consuming
microprocessor inside the PCM. The fuel level indicator, fuel tank pressure, and battery voltage are
inputs to the microprocessor. The microprocessor outputs are the CV solenoid and the stored test
information. If the separate microprocessor is unable to control the CV solenoid or communicate with
other processors DTC P260F is set.
6. The MIL is activated for DTCs P0456 and P260F. The MIL can also be activated for any enhanced
EVAP system component DTCs in the same manner. The enhanced EVAP system component DTCs
P0443, P0446, P0452, P0453, and P1451 are tested as part of the CCM.